The present invention relates to an electrolytic process for dissolving platinum, platinum metal impurities and/or platinum metal alloys, in particular which contain Rh, Pd, It, Au and/or Ag, in aqueous hydrochloric acid.
The platinum metals can be present in the form of solid bodies, e.g. as granulated metal, sheet metal, shavings, wire and the like.
The process according to the invention can, however, also be used to dissolve powders, silts and noble metals present in ceramics, quartz components, aluminum oxide or silicates.
The use of chlorine gas and hydrochloric acid to dissolve platinum and/or platinum metal alloys is generally known (Gmelin, Platin, Section C, page 77).
In Ullmann, Enzyklopadie der Chemie, Vol. 18, 1979, page 708, chlorine and hydrochloric acid is used for powders, silts and ore concentrates. The process operates with a 6 to 8N hydrochloric acid at a temperature of 80.degree. C. It was observed, inter alia, that dissolved platinum metals hereby do not reduce the dissolution rate.
According to the German Patent Document DD-63880, platinum metals in the form of granulated metal, sheet metal or wire can be dissolved with chlorine and hydrochloric acid. The platinum metal salts or platinum metal acids thus formed are washed with aqueous hydrochloric acid. The hydrochloric acid and the chlorine gas are added in an alternating manner. The process operates with a constantly diminishing platinum surface. Targetted addition of hydrochloric acid is not possible. Therefore it is also impossible to produce concentrated noble metal solutions. In the case of reduced amounts of platinum metal, it is necessary to perform the process with a high chlorine surplus.
Due to the sequence of process steps, the achievable concentration of 500 g/l platinum metal and the dissolution rate of 1000 g/h described in the DD-63880 are reached only in exceptional cases. Moreover, the minimum amount of platinum metal that can be processed by the method of DD-63880 is 4 to 6 kg.
All described prior art processes have the disadvantage that, due to the use of chlorine gas with its dosage problems, they require elaborate machinery and safety technology. They are very expensive and ecologically no longer acceptable.